Thanks a lot for the reply. I tried a few different things since my first post, but I'm still at it... slowly figuring it all out.
I tried running power from the battery straight to the head unit using a 10 gauge wire with an in-line 10A fuse. I spliced the head unit's power and memory leads together and connected them to that 10A fuse protected line.
Everything worked perfectly for a couple of days, but the head unit eventually wound up draining my battery (and it's a relatively new battery), even though I made sure the head unit was powered off when the car wasn't running.
This surprised me a bit because that is essentially how my old radio was connected, and that old radio never drained the battery. I guess these newer head units work differently?
In any event, I've obviously abandoned that approach and am now going to keep the memory and power leads separate. I took a closer look at my fuse box and identified the switched and unswitched fuses. This brings me to your answer to my first question:
1. Why are the orange and red wires together?? Is that bad? And why are they using two different types of fuses?
A: no idea. They're both hot? Your radio will need a switched and unswitched 12v+. Switched is when you turn on the key, it turns on the radio. Unswitched keeps your radio's memory going while the car is off, very little draw there so now worries if your battery is healthy. Need to determine if these two are live when the key is turned on or if they're always hot. IMO what the previous owner did was put BOTH switched and unswitched from the harness to the on the unswitched 12v+ on the car so that you can listen to the radio with the car off. No problems with this as long as your battery and charging system is healthy and you don't overdo it. Other than that, make sure you have an excellent ground wire, as short as possible, that makes great contact with the body.
Both of the wires that were connected to the old radio have constant unswitched power. Did a little investigating, and it looks like those wires (which are spliced together) are tied to fuse #5, which is an 8A fuse. I agree with you... I think the previous owner wanted to be able to listen to the radio with the car turned off. I used that radio for years without any battery drainage issues, but it appears that that approach will not work with this newer Alpine unit.
So, STEP #1 CONNECTING THE MEMORY LEAD: I'm going to remove the old splice, and connect that constant unswitched power (coming off fuse #5) to the Alpine's memory lead. That should work, right? My only concern is that fuse #5 is an 8A fuse, and the Alpine might need 10A (judging from the 10A fuse on the unit), but maybe for memory 8A is enough?
STEP #2 CONNECTING THE POWER LEAD: Fuses #6, #7, #8 are all 8A fuses and have switched power (tied to the ignition). I believe I need up to 10A to power the head unit. I therefore located the wire going INTO fuse #6, and spliced a separate wire to it, bypassing the 8A fuse. I plan on installing an in-line 10A fuse on that spliced wire and connecting that 10A fused wire to the power lead on the head unit.
This brings me to this...
3. Do I need in-line spring-loaded fuses? I noticed there's a 10A fuse holder in the back of the Alpine Head Unit... does that mean I don't need other fuses?
A: No, your leads come from the fuse box and there's one in the back of the head unit, so you're covered.
Just wanted to clarify, so I don't actually need in-line fuses?
Thanks for the help!